NOx sensor – what is a nitric oxide sensor and how does it work?

Internal combustion vehicles and agricultural machinery must now be equipped with nitrogen oxide sensors. The general purpose of using these components, which are part of the SCR (Selective Catalytic Reduction) system, is to reduce the amount of harmful substances that are released into the atmosphere in the exhaust gas, while their specific function is to control the amount of nitrogen oxides. In this blog post, you will learn what NOx sensors are, how they work and what they do in your vehicle.

NOx sensor functions


The function of NOx sensors is to measure the concentration of the most common nitrogen oxides in the exhaust gas. These gases are nitrogen oxide (NO) and nitrogen dioxide (NO2). The sensors are mounted in front of the catalytic converter or behind it – it depends on the SCR system design in a given vehicle model. The detection of nitrogen oxides is not the only function of the sensors, because thanks to them you can also:


– detect the initial causes of failure of the exhaust gas treatment system;
– learn about the need for system maintenance;
– identify components that require replacement;
– refill the Adblue tank.

Why is the detection of nitrogen oxides so important?


Nitrogen oxides are one of the most harmful compounds that are emitted into the atmosphere together with exhaust fumes. Their high concentration is a real health hazard. Due to their high harmfulness to the natural environment, manufacturers of internal combustion vehicles as well as construction and agricultural machinery must meet certain standards that force them to install exhaust gas recirculation systems in vehicles. Thanks to them, it is possible to reduce the emission of harmful substances in the exhaust gas. Recirculation systems improve the environmental friendliness of vehicles not only by purifying exhaust gases from nitrogen oxides, but also optimizing engine operation and reducing fuel consumption.

Recommended products:

How do NOx sensors work?


The nitrogen oxides sensor is located in the exhaust system, where it continuously measures the NOx concentration in the exhaust gas. Information about the concentration is then sent to the engine controller, which on their basis determines the optimal parameters of the drive unit and doses the appropriate amount of Adblue, trying to minimize the emission of harmful nitrogen compounds.
The NOx sensor contains an active electrode that catalyzes nitrogen oxides, breaking them down into nitrogen and oxygen. The sensor is also equipped with two chambers – in one of them the oxygen content is kept constant, which is about 10 ppm, and in the other, the aforementioned NOx catalysis takes place. In order to maintain the environmental properties of the platinum-rhodium anaerobic electrode, a current with values ​​proportional to the concentrations of nitrogen oxides is used. It is this electrical impulse that is responsible for sending the measuring signal.

Faults in NOx sensors


Damaged oxide sensors will release harmful nitrogen compounds into the atmosphere with the exhaust gas. In addition, they will cause engine malfunctions and increase fuel consumption.
The location of NOx sensors is conducive to mechanical and thermal damage. The diagnosis of the efficiency of sensors should begin with checking the condition of the wiring, because it may turn out that damaged cables do not provide correct information about the measurements.


In case of faults, the mixture of optimal composition will not be fed to the engine. In such a situation, its performance will decrease and fuel consumption will increase.


If the computer diagnostics system detects any faults in the NOx sensor, it must be replaced with a new one. In the Acoore offer you will find new NOx sensors equipped with a digital signal – very good quality replacements, compatible with the ECU software of trucks. We have NOx sensors for all vehicles and trucks of all brands: MAN, Scania, Mercedes, Volvo, Iveco, Renault, DAF and buses Solaris, Bova, MAN, Irizar.